Gravity filtration systems generally comprise a filter bed of one or more granular filter media. A liquid is filtered by flowing downwardly through the filter media and through openings in a filtration tank or underdrain disposed below the filter media. The gravity filtration system is cleaned by backwashing air and/or water from the filtration tank or underdrain in a direction opposite to the flow of liquid during the filtration process. It is extremely important for the backwash to have an even distribution. A nonuniform backwash flow can fail to clean parts of the filter media and can disrupt the filter bed, which reduces the life of the filtration system.
The only low-cost underdrain currently on the market requires extensive grout work during installation and is therefore fairly difficult to install. There is a need for an underdrain which is inexpensive, easy to install and easily adaptable to different applications.